Pull boxes space used along with conduit to simplify wiring installation, thus their name. They are made of sheet metal, actors metal, or a non-metallic material, and administer a method to pull conductors long distances without placing extreme strain top top the cable or insulation. Traction boxes allow long wiring runs to be mounted in shorter intervals, and can be used for both straight and angled pulls.
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Although they have actually the exact same appearance as junction boxes, traction boxes perform not have actually wiring relations inside. They are only accessibility points because that pulling and feeding conductors right into a raceway system. Their use is mandatory in conduit runs where the number of bends in between outlets above the preferably number permitted by the NEC (National electric Code).
Pull box sizing is based on the dimension and variety of conductors, and also the variety of raceways and their diameter. Because that conductors 4 AWG and larger, traction boxes and junction boxes must be size in accordance v NEC write-up 314.28. This article will administer an outline of the sizing rules for the many common types of pulls, in addition to a calculation example.
In directly pulls, conduit enters and also leaves ~ above opposite sides of the box. The depth of a crate for a right pull is figured out by the dimension of the biggest conduit and by room required by locknuts and bushings. Top top the other hand, the traction box size must be at the very least eight time the diameter of the largest conduit:Assume a pull box has four conduit runs, and the biggest diameter is 4”Minimum box size = 8 x 4” = 32”
Angle Pulls, U-Pulls and also Splices
Boxes and conduit bodies containing conductors 4 AWG or larger, and also containing angle or U-pulls should be size in accordance through the specifications of NEC write-up 314.28(A)(2).
For edge pulls, the distance between each raceway entry within the box and the opposite wall surface of the box must be the sum of the following:Six times the trade size of the biggest raceway in a row. The amount of the diameters of all other raceway entries in the row.
Assume a pull box has actually a 90° revolve with three raceways, through diameters 4”, 2” and also 2”. The calculation procedure would certainly be as follows:Six times the largest raceway diameter = 6 x 4” = 24”Sum that all various other raceway diameters = 2” + 2” = 4”Total = 24” + 4” = 28”
In addition, the directly distance between the entry and also exit point out of every circuit have to be six times the corresponding conduit diameter. In the example above, the required separations are:Separation because that circuits in 4” conduit = 6 x 4” = 24”Separation because that circuits in 2” conduit = 6 x 2” = 12”
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When conductors enter and leave indigenous the exact same wall, the distance from whereby the raceways go into to the opposite wall surface is calculated with the very same procedure used for angle turns:Six times the trade dimension of the biggest raceway in a row. The amount of diameters for all various other raceways on the same wall and row.
Note that the entry and also exit points room counted separately because that each conductor run. If a circuit supplies 3” conduit and also uses a pull crate for a u-turn, the procedure is together follows:Six times the largest raceway diameter = 6 x 3” = 18”Sum of all other raceway diameters = 3”Total = 18” + 3” = 21”
The straight-line distance between the entry and exit point is just like in edge turns: 6 times the conduit diameter. In the example above, the forced separation is 18” (6 x 3”).
Combination Boxes v Straight and Angle Pulls
When there are straight and angle traction in the exact same box, the calculations need to be performed according to both sets of rules, and also the largest resulting measurement applies. I think the following combination pull:Straight pull through a 2” racewayAngled pull through a 3” raceway
This calculation is straightforward due to the fact that there is just one possibility: six times the largest raceway to add the amount of the rest. Over there is just one raceway, so it is multiplied by six and also nothing else is added.Height = 6 x 3” = 18”
In this instance there are two possibilities, therefore both calculations are performed and also the biggest value is chosen. Choice #1 is 8 times the diameter because that the straight pull, and Option #2 is 6 time the biggest raceway to add all other diameters.Width (Option 1) = 8 x 2” = 16”Width (Option 2) = 6 x 3” + 2” = 18” + 2” = 20”
Pull crate Dimensions
This pull box must have a elevation of 18” and also a broad of 20”. Because that the angle pull, the distance between the entry and exit is 18” (six times the conduit dimension, which is 3”).
Importance of the design Procedure
While traction boxes room convenient, keep in mind that they call for materials and also labor, and can rise project expense if provided excessively. The ideal recommendation is to hire a qualified style firm come optimize the electrical layout, ensuring the pull boxes space only used where necessary.
Energy efficiency additionally helps optimize electric installation costs. A lower pack requires smaller sized wiring, which subsequently uses smaller sized a smaller sized conduit diameter and accessories. The price difference may not be much for a solitary circuit, yet quickly adds increase in a large project such together a high-rise building.
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Editors Note: This write-up was originally published in November 2017 and also has to be revamped and also updated for accuracy and also comprehensiveness.